[PATCH 6.4 503/800] modpost: fix section mismatch message for R_ARM_{PC24,CALL,JUMP24}

Greg Kroah-Hartman
2023-07-16T20:16:22Z

From: Masahiro Yamada <masahiroy@kernel.org>

[ Upstream commit 56a24b8ce6a7f9c4a21b2276a8644f6f3d8fc14d ]

addend_arm_rel() processes R_ARM_PC24, R_ARM_CALL, R_ARM_JUMP24 in a
wrong way.

Here, test code.

[test code for R_ARM_JUMP24]

.section .init.text,"ax"
bar:
bx lr

.section .text,"ax"
.globl foo
foo:
b bar

[test code for R_ARM_CALL]

.section .init.text,"ax"
bar:
bx lr

.section .text,"ax"
.globl foo
foo:
push {lr}
bl bar
pop {pc}

If you compile it with ARM multi_v7_defconfig, modpost will show the
symbol name, (unknown).

WARNING: modpost: vmlinux.o: section mismatch in reference: foo (section: .text) -> (unknown) (section: .init.text)

(You need to use GNU linker instead of LLD to reproduce it.)

Fix the code to make modpost show the correct symbol name.

I imported (with adjustment) sign_extend32() from include/linux/bitops.h.

The '+8' is the compensation for pc-relative instruction. It is
documented in "ELF for the Arm Architecture" [1].

"If the relocation is pc-relative then compensation for the PC bias
(the PC value is 8 bytes ahead of the executing instruction in Arm
state and 4 bytes in Thumb state) must be encoded in the relocation
by the object producer."

[1]: https://github.com/ARM-software/abi-aa/blob/main/aaelf32/aaelf32.rst

Fixes: 56a974fa2d59 ("kbuild: make better section mismatch reports on arm")
Fixes: 6e2e340b59d2 ("ARM: 7324/1: modpost: Fix section warnings for ARM for many compilers")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
scripts/mod/modpost.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 6c2371f684a94..d97cbd753d2c3 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1411,12 +1411,20 @@ static int addend_386_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
#define R_ARM_THM_JUMP19 51
#endif

+static int32_t sign_extend32(int32_t value, int index)
+{
+ uint8_t shift = 31 - index;
+
+ return (int32_t)(value << shift) >> shift;
+}
+
static int addend_arm_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
{
unsigned int r_typ = ELF_R_TYPE(r->r_info);
Elf_Sym *sym = elf->symtab_start + ELF_R_SYM(r->r_info);
void *loc = reloc_location(elf, sechdr, r);
uint32_t inst;
+ int32_t offset;

switch (r_typ) {
case R_ARM_ABS32:
@@ -1426,6 +1434,10 @@ static int addend_arm_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
case R_ARM_PC24:
case R_ARM_CALL:
case R_ARM_JUMP24:
+ inst = TO_NATIVE(*(uint32_t *)loc);
+ offset = sign_extend32((inst & 0x00ffffff) << 2, 25);
+ r->r_addend = offset + sym->st_value + 8;
+ break;
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24:
case R_ARM_THM_JUMP19:
--
2.39.2